1. Field of the Invention
This invention relates to a device for printing letters, marks and the like on tablets or capsules (hereinafter referred to as tablets).
2. Prior Art
A tablet printing device of the construction shown in FIG. 2, for example, is well known. This tablet printing device 1 comprises a rotary cylinder 2, a hopper 10 above said cylinder 2, a printing roller 11 and a chute 15 below the cylinder 2. The rotary cylinder 2 has at its periphery many recesses 3 in which tablets T are received. The rotary cylinder 2 is provided with air holes which open to one side and each air hole 4 is connected to a nozzle hole 5 which opens to a recess 3, as shown in FIG. 4. Numeral 6 in FIG. 3 is a plate for air distribution which is in tight contact with the rotary cylinder 2 and communicates with a vacuum device and a source of pressurized air (these are not shown in the drawing). Plate 6 has a groove opposed to the air holes 4. By this arrangement, the recesses 3 are subjected to sucking action by the vacuum device while they move from the exit of the hopper 10 to the inlet of the chute 15 but are subjected to discharge action by pressurized air while they are opposed to the chute 15.
Printing roller 11 comprises, as an example, a printing type roller 12 having the required letters, marks or the like which project from its periphery and a transfer roller 13 which is made of elastic material, such as rubber, and makes contact with the printing type roller 12. Printing type of printing type roller 12 are supplied with ink from an ink tank 14 and ink on the printing type is transferred to the transfer roller 13, which prints the surfaces of tablets. In this case, if a table T is flat and has an even surface C at its side, such tablet sometimes will not be received accurately in the recess 3. As shown in FIG. 4, a tablet Ta is received in a recess 3 in a regular state, but a tablet Tb is received in a recess 3 in a abnormal state, namely, received in the recess at a right angle in relation to the tablet Ta. Both of the tablet Ta and the table Tb are carried to the transfer roller 13 in the positions shown in the drawing and then are printed. This means that the tablet Tb is printed at its side or sucking action is not applied fully to the Tablet Tb, with the result that the tablet Tb falls off the rotary cylinder 2 and is sandwiched between the rotary cylinder 2 and the transfer roller 13, thus causing operating problems.
In any case, it is not desirable that the tablets T be received in the recesses 3 in abnormal states and it is necessary to have all tablets received in regular positions in the recesses. However, it is very difficult to ensure that all tablets are received accurately in the recesses.